Thermal stability in vacuum and in air of Al/Ni/W based ohmic contacts to p-type SiC

The Al/Ni/W contact demonstrated excellent thermal stability after being aged at 600 degreesC in a high vacuum of 1x10(-6) mmHg for 1022 hours. No degradation in contact resistivity was found after the aging. However, 1 hour aging in air severely degraded the ohmic characteristics of the Al/Ni/W contact. An Al/Ni/W/Mo contact showed ohmic behavior at 300 degreesC in air for 186 hours, while an Al/Ni/W/Au contact displayed good thermal stability at 600 degreesC in air for over 100 hours. In order to avoid the problem of metal oxidation in air and at elevated temperatures, we have proposed and tested a new approach to improving the in-air thermal stability of the Al/Ni/W ohmic contact by adding a top conductive oxide layer to the contact.